1. Field of the Invention
The present invention relates to a mowing apparatus with a mowing head including a rotational member and flexible cutting lines which are fitted to the rotational member and rotate with the rotational member around the mowing head, thereby grass and the like are cut by the rotating cutting lines.
2. Description of the Prior Art
There are two general classification types for conventional mowing apparatus which can be identified in accordance with their cutting devices. In one of those types, a disk-shaped cutter which is formed with a large number of cutting teeth on the outer periphery thereof is mounted on a mowing head as a cutting device and it is rotated in order to cut grass with the cutting teeth. In the other type, a few lines made of strong and flexible material such as nylon and the like are provided on a mowing head, and these lines are rotated at a high speed around the mowing head to cut grass with the free ends of the lines. In comparing these two types, it can be easily understood that the line-cutting type is more advantageous in operational safety than the disk-cutting type.
U.S. Pat. No. 3,708,967 of Geist et al. issued on Jan. 9, 1973 discloses an example of the line-cutting type mowing apparatus. This mowing apparatus comprises a mowing head having a rotational member with reel members. For every reel member, a long cutting line is wound thereupon, and the free end of the cutting line extending from the reel is rotated around the mowing head by the rotational member which is rotated relative to the mowing head by a drive source. If the cutting line is worn out, an appropriate length of the cutting line is pulled out from the reel member in order to use a fresh portion of the cutting line.
However, In recent years strength and durability of the line cutter have been remarkably improved in accordance with development of material technology. Therefore, wear of the cutting line caused by use is reduced so that it is no longer required to frequently supply a fresh cutting line. Moreover, for promoting easy operation, a light and small mowing head is preferred. As a result, a modification to the line-cutting type mowing apparatus has been employed lately; in which the reel is omitted and each of the cutting lines, with an appropriate length, are directly secured to the rotational member. In this modification, if the line cutter is worn out, it is removed and changed with a fresh one.
A mowing apparatus with the above-described structure is disclosed, for example, in FIGS. 1 to 4 of U.S. Pat. No. 4,190,954 of Mar. 4, 1980 by Walto. This mowing apparatus comprises two lines and the intermediate portions of the lines are tied to each other at the center of a disk type rotational member on the lower surface thereof so that the terminal ends of the lines can radially extend from the rotational member at equal angular intervals between each line.
Moreover, FIGS. 5 and 6 of U.S. Pat. No. 4,190,954 also disclose another example. In this example, the central portions of the lines are not tied together but retained in curved recesses on the rotational member.
In connection with the mowing apparatus of the above-described mode, there are some highly important issues. First, the cutting lines must be easily set to the rotational member and they must also be firmly retained on the rotational member after the setting so that the cutting lines can be prevented from moving and coming off the rotational member. Second, since the free ends of cutting lines, during cutting operation, are always pulled outwards by centrifugal force and resistant or frictional forces caused by the grass being cut and the like, it is necessary to prevent such stress from being concentrated on a specific portion of the cutting line (e.g. the portion of the cutting line which the line is restrained to the rotational member) to prohibit failure due to the concentrated stress, before the free ends of the line get worn down.
Concentrating on the above-described issues, it can be seen that the first example of U.S. Pat. No. 4,190,954 is prone to fall with respect to the second issue. Specifically, the lines may be easily cut off at the tied portions, because two cutting lines are pulling against each other, thereby the tensile force will be localized in the entangled portions. Moreover, since the lines of this example pass through the center of the rotational member, it is impossible to modify the arrangement, such as to attach the lines to the upper side of the rotational member. As a result, the mowing head of the apparatus must be turned upside down for replacement of the cutting lines.
On the contrary, the second example of U.S. Pat. No. 4,190,954 can solve the problems contained in the second issue. However, It is disadvantaged in solving the problems of the first Issue described above, because the cutting lines may easily move or come off the rotational member. Especially, when a somewhat hard or thick cord is used and set to the rotational member as a cutting line, the cord will likely move due to the force acting within the bent portions of the cord to return it to its natural straight state.
As described above, the conventional line-cutting type mowing apparatus cannot meet the following criteria fully, easy replacement and firm restraining of the cutting lines and prevention of local concentration of stress in the cutting lines.